Recently, as mobile phones and the Internet have been widely used, the amount of data to be handled is increased. As such, it is advantageous to process a large amount of data at a higher speed. In such a situation, as a system for storing a large amount of data, a demand for a key value store (KVS) is increasing. In a key value store, data (value) is associated with a unique sign (key), and they are stored in a pair. Hereinafter, data in which a key and a value are paired is called KV data. In particular, a system having a function capable of storing units of KV data distributedly in a plurality of servers is called a distributed KVS. A distributed KVS, which is a type of a distributed database, is mainly used in a system not requiring data consistency strongly but focusing on scalability and throughput.